The present invention relates to a distance-measuring system capable of measuring a distance of a target from the system in an optical way, and, more particularly, to a compact, lightweight and cheap structure of such a system.
For determining the distance of a target from the distance-measuring system a variety of technologies are available. These technologies usually involve emitting some type of radiation (e.g. light, supersonic and radar) towards the target and receiving a portion of the radiation reflected back from the target. The distance from the system to the target is determined by one of several approaches well known by the skilled person; detailed description is therefore omitted. Some examples are described in prior art documents U.S. Pat. No. 4,113,381, U.S. Pat. No. 5,241,360, U.S. Pat. No. 6,765,653 or US 2004/0246461. For example, some systems calculate the distance from the system to the target by determining a phase difference between radiation emitted to the target and reflected radiation received from the target, while other systems measure a time delay between emission of the radiation to the target and receipt of the reflected radiation at the system. For example, measurement of distance can be accomplished by emitting a modulated microwave or infrared carrier signal to the target that is reflected by the target. The distance can then be determined, for example, by emitting and receiving multiple frequencies, and determining the integer number of wavelengths to the target for each frequency.
Such systems according to the above prior art, which use light as radiation, usually comprise a light source, a light detector and measuring optics for projecting light emitted by the light source to the target and for guiding light reflected from the target back towards the light detector.
The target can be a so-called non-cooperative target having comparatively low reflectivity (e.g. a wall of a building, a stone, a tree, or other environmental object), or a so-called cooperative target having comparatively high reflectivity (e.g. a prism or reflector). To adapt the light detector to varying intensities of reflected light that is received from different targets, the system often further comprises a variable attenuator for adjusting the intensity of light incident on the light detector.